No methods are known to be in use or to have been disclosed which are directed either to controlling consistency in the feed to the washing surface and in the pulp mat formed thereon or to controlling the weight of plup mat (on a dry basis) per unit area on the washing surface.
Methods as follows are used in drum washing systems to control drum speed and the rate of dilution liquid stream flow into the washer vat (vat dilution liquid flow).
In a first method, an operator uses his experience and information from inlet conditions into the first stage of the washing process, his observation of washer vat levels and his estimate of consistency in the washer vat, to manually adjust rotational speed of the washer drum and vat dilution liquid flow.
In a second method, washer drum rotation speed is controlled automatically in response to sensing of liquid level in the washer vat, and vat dilution liquid flow is adjusted manually by the operator based on his experience and information from the inlet conditions into the first stage of the washing process.
In a third method, the washer drum rotation speed is manually set by the operator based on his experience and information from the inlet conditions into the first stage of the washing process and vat dilution liquid flow is automatically controlled in response to sensing of liquid level in the washer vat to maintain a selected liquid level in the washer vat.
These three methods fail to control consistency in the washer vat or weight of pulp mat (on a dry pulp basis) on the washer drum. In these methods, normal process swings in tonnage rates entering the first stage increase or decrease the consistency in the liquid in the washer vat and the pulp weight per unit area on the washer drum and these increase and decreases cause inefficiencies in the washing process.